Multiply the following complex numbers, marked as blue dots on the graph: $(2 e^{5\pi i / 6}) \cdot (2 e^{3\pi i / 2})$ (Your current answer will be plotted in orange.)
Answer: Multiplying complex numbers in polar forms can be done by multiplying the lengths and adding the angles. The first number ( $2 e^{5\pi i / 6}$ ) has angle $\frac{5}{6}\pi$ and radius $2$ The second number ( $2 e^{3\pi i / 2}$ ) has angle $\frac{3}{2}\pi$ and radius $2$ The radius of the result will be $2 \cdot 2$ , which is $4$ The sum of the angles is $\frac{5}{6}\pi + \frac{3}{2}\pi = \frac{7}{3}\pi$ The angle $\frac{7}{3}\pi$ is more than $2 \pi$ . A complex number goes a full circle if its angle is increased by $2 \pi$ , so it goes back to itself. Because of that, angles of complex numbers are convenient to keep between $0$ and $2 \pi$ $\frac{7}{3}\pi - 2 \pi = \frac{1}{3}\pi$ The radius of the result is $4$ and the angle of the result is $\frac{1}{3}\pi$.